Lead batteries have been used in various applications, such as starting of automotive engines and back-up power source. The amount of self-discharge of lead batteries is smaller than that of alkaline storage batteries. However, when lead batteries are stored for an extended period of time during their distribution process, their self-discharge may proceed such that they need to be recharged when they are used. Therefore, further suppressing the self-discharge of lead batteries is still an important technical problem to be solved.
Lead batteries have positive and negative electrode plates each including a grid, and the grid is often made of a Pb—Sb based alloy or a Pb—Ca based alloy. The self-discharge characteristics of batteries vary with the alloy type of the grid. Although Pb—Sb based alloys have good casting characteristics and high strength, the presence of Sb increases the self-discharge.
Thus, lead batteries using a Pb—Sb based alloy in the grid are stored by the following methods. One method is to store batteries that are assembled using formed electrode plates, which have been subjected to a formation treatment and dried in a production process of the electrode plates (see Patent Document 1). Another method is to inject an electrolyte into a battery assembled using unformed electrode plates, perform formation in the battery container, then discharge the electrolyte contained in the battery container, and store the battery with the electrolyte discharged.
In the case of lead batteries using a Pb—Sb based alloy in the grid, by storing them in the above manners and injecting an electrolyte immediately before using them, it is possible to prevent self-discharge during a long-term storage of unused batteries. However, there still remains a problem of being unable to suppress the self-discharge once the electrolyte is injected.
On the other hand, the use of a Pb—Ca based alloy in the grid can decrease the amount of self-discharge of the resultant lead battery to approximately ½ to ⅓ that of a battery using a Pb—Sb based alloy in the grid. However, if the ambient temperature becomes high during storage of batteries, the batteries are apt to self-discharge. Thus, even batteries using a Pb—Ca based alloy self-discharge during storage, so that they may need to be recharged when they are used. For example, in Japan, when batteries are stored for an extended period of time in a non-air-conditioned warehouse, the temperature inside the warehouse often rises to 40° C. or more during summer. Hence, batteries may need to be recharged every several months.
To recharge the batteries, they need to be unpacked, then recharged, and packed again. Since such procedure must be done manually, it takes an enormous cost for facilities and electric power necessary for recharging and an enormous time for recharging. This results in an increase in the distribution cost of batteries.
Patent Document 1: Japanese Laid-Open Patent Publication No. Sho 52-93930